Drag bit



DRAG BI T Filed June 19, 1962 5 Sheets-Sheet l "-3! i 1 50 36 --30 LL HAROLD G. BRIDWELL EVERETT H. LOCK INVENTORS BY %.-..Q a. M

ATTORNEY y 7, 1966 H. c. BRIDWELL ETAL 3,251,425

DRAG BIT 5 Sheets-Sheet 2 Filed June 19, 1962 FIG. ll

FIG

HAROLD C. BRIDWELL EVERETT H. LOCK INVENTORS FIG. IO

ATTORNEY May 17 1966 H. c. BRIDWELL ETAL 3 251 425 DRAG BIT Filed June 19, 1962' 5 Sheets-Sheet 3 HAROLD C. BRIDWELL EVERETT H. LOCK INVENTORS BY 2......) Q-k ATTORNEY May 17, 1966 Filed June 19, 1962 H. C. BRIDWELL ETAL DRAG BIT 5 Sheets-Sheet 4 1 I32 i I46 i HAROLD c. BRIDWELL EVERETT H. LOCK INVENTORS A TTO RNEY y 7, 1966 H. c. BRIDWELL ETAL 3,251,425

HAROLD C BRIDWELL EVERETT H. LOCK INVENTORS BY .MJaQA ATTORNEY United States Patent 3,251,425 DRAG BIT Harold C. Bridwell and Everett H. Lock, Tulsa, Okla, assignors, by mesne assignments, to Esso Production Research Company, Houston, Tex., a corporation of Delaware Filed June 19, 1962, Ser. No. 203,601

17 Claims. ((11. 175-279) The present invention relates to rotary bits useful for drilling boreholes in the earth and is particularly concerned with an improved drag bit which will generally permit higher overall drilling rates than can be obtained with drag bits available in the past.

Drag bits used in the petroleum industry are normally sharpened by the manufacturer to provide a small clear ance angle beneath the trailing edge of each blade. Such an angle reduces the blade contact area at the bottom of the borehole, permits greater penetration into the formation under a given load, and makes possible higher initial drilling rates than might otherwise be obtained. As the blades wear away, this clearance angle is reduced until the bottom of each blade fully contacts the formation. Loss of the clearance angle is generally accompanied by a marked reduction in drilling rates. a point may be reached where the bit will no longer drill at all. The loadings required to secure penetration with the dullblades lead to prohibitive torque requirements and produce stresses which cause blade failure. It is thus essential that a clearance angle be maintained beneath the blades throughout the life of the bit. Efforts to do this have been largely unsuccessful. Repeated sharpening at the earths surface is generally impractical because of the cost of frequent trips into and out of the bore-' hole. Satisfactory methods for sharpening the blades without removing the bit from the hole have not been developed. It is therefore generally necessary to restrict the use of drag bits to drilling operations in areas where soft formations are apt to be encountered and to employ roller cone bits. in areas where hard formations must be penetrated.

It is an object of the present invention to provide an improved drag bit which will permit higher overall drilling rates than have generally been obtained with drag bits available in the past. A further object is to provide a drag bit which can be used effectively for long periods in hard formations. Another object is to provide a bit which can readily be sharpenedduring rotary drilling operations to maintain an effective clearance angle. Still another object is to provide a drag bit which can be re peatedly sharpened within the borehole. Other objects will become apparent as the invention is described in detail hereafter.

In accordance with the invention, it has now been found that difficulties encountered in maintaining an effective clearance angle beneath the blades of drag bits available in the past can largely be avoided by utilizing bits fitted with movable blades which can be shifted into a sharpening position with respect to the formation at the bottom of the borehole. By rotating the bit in contact with the formation with the blades in this position, the trailing edges can be ground off to restore the required clearance angle. Once this has been done, the blades can be returned to the normal drilling position and drilling can be resumed. The use of such a bit makes possible repeated sharpening of the blades without removing the drill string from the borehole and often permits significantly higher overall drilling rates than might otherwise be obtained.

The exact nature and objects of the invention can best be understood by referring to the following detailed description of several preferred embodiments and to the accompanying drawing, in which:

In hard formations,.

ice

FIGURE 1 is a vertical elevation, partially in section, of a drag bit provided with movable blades actuated by the application of suflicient torque to overcome the effect of a preloaded torsional member within the body of the bit;

FIGURE 2 is a cross-sectional view of thebit shown in FIGURE 1 taken about the line 2-2 in FIGURE 1;

FIGURE 3 is a bottom view of the bit shown in FIG- URE 1;

FIGURE 4 is a fragmentary vertical section through a bit of the type shown in FIGURE 1 depicting the use of an alternate type torsional member;

FIGURE 5 is a fragmentary vertical elevation of the bit of FIGURE 1 rotated showing the blades of the bit in the sharpening position;

FIGURE 6 is a fragmentary vertical elevation of the bit of FIGURE 1 rotated 90, showing the blades of the bit in the normal drilling position;

FIGURE 7 is a vertical elevation, partially in section, of a drag bit provided with movable blades which are. actuated by changing the weight applied to the tool;

FIGURE 8 is a fragmentary vertical elevation, partially in section, showing the nozzles and other details of the bit of FIGURE 7;

FIGURE 9 is a cross-section through the bit of FIG- URE 7 taken about the line 9-9 in FIGURE 7;

FIGURE 10 is a bottom view of the bit of FIGURE 7;

FIGURE 11 is a fragmentary vertical elevation of the bit of FIGURE 7 rotated 90, showing the blades of the bit in the sharpening position;

FIGURE 12 is a fragmentary vertical elevation of the bit of FIGURE 7 rotated 90, showing the blades of the bit in the drilling position;

FIGURE 13 is a vertical elevation, partially in section, of anothed drag bit provided with movable blades actu ated by a change in the bit weight applied to the tool;

FIGURE 14 is a cross-sectional view of the bit shown in FIGURE 13 taken about the line 14-14 in FIGURE FIGURE 15 is 'a cross-sectional view of the bit shown in FIGURE 13 taken about the line 15-15 in FIGURE 13;

FIGURE 16 is a bottom view of the bit shown in FIG- URE 13;

FIGURE 17 is a fragmentary vertical elevation of the bit shown in FIGURE 13, rotated 90, with the blades in the normal drilling position; 7

FIGURE 18 isa cross-sectional view of the bit shown in FIGURE 17 taken about the line 18-18 in FIGURE 17;

FIGURE 19 is a fragmentary vertical elevation of the bit shown in FIGURE 13, rotated 90", with the blades in the sharpening position;

FIGURE 20 is a vertical elevation, partially in section, of a bit provided with movable blades shaped to form a convex surface at the bottom of the borehole;

FIGURE 21 is a fragmentary view of the bit of FIG- URE 20, rotated 90, showing the blades in the normal drilling position;

FIGURE 22 is a fragmentary view of the bit of FIG- URE 20, rotated 90, showing the blades in the sharpening position;

FIGURE 23 is a fragmentary vertical elevation, partially in section, of a bit provided with movable blades shaped to form a concave surface at the bottom of the borehole; 1

FIGURE 24 is a fragmentary view of the bit of FIG URE 23, rotated 90, showing the blades in the normal drilling position;

FIGURE 25 is a fragmentary view of the bit of FIG- URE 23, rotated 90, showing the blades in the sharpening position;

FIGURE 26 is a fragmentary sectional view of the upper end of a bit of the type shown in FIGURE 13 provided with a device for locking the blades in the drilling position;

' FIGURE 27 is a cross-sectional view through the bit of FIGURE 26 taken about the line 2727 in FIGURE 26; and,

FIGURE 28 is a fragmentary sectional view of the bit of FIGURE 26 showing the locking device in the unlocked position.

The bit depicted in FIGURE 1 of the drawing includes a steel connecting member 11 located at the upper end of the tool. The connecting member shown is provided with an upper shank 12 and external threads 13 to form a standard A.P.I. tool joint pin. In lieu of such a pin, a box or other means for connecting the apparatus to the lower end of a rotary drill string may be provided. An axial passageway 14 extends through the connecting member for the introduction of drilling fluid from the drill string into the tool. Internal shoulders 15, 16 and 17 are located in the bore of the connecting member and face the lower end of the tool. An external shoulder 18 is located on the outer surface of the connecting member above a lower section of reduced diameter provided with threads 19. Outer barrel 20 is attached to the connecting member by means of threads which mate with those on the connecting member. The outer barrel is an elongated tubular steel member provided with an intermediate section 21 of reduced internal diameter which is bounded by an upper shoulder 22 and a lower shoulder 23 within the barrel. Below the lower shoulder, the bore of the outer barrel is of generally octagonal cross-section as shown in FIGURE 2 of the drawing. Slots 24, located on the lower edge of the outer barrel, are shown more clearly in FIGURES 5 and 6 of the drawing.

Inner barrel 25 on the bit shown in FIGURE 1 is a tubular steel member positioned in the upper part of the outer barrel below the connecting member. The upper end of the inner barrel extends upwardly adjacent shoulder 15 on the connecting member. A seal between the two is provided by packing 26 of rubber, plastic or similar material. The packing is held in place by an annular retainer 27, which is in turn secured by bolts 28, only one of which is shown. A series of slots 29, indicated by hidden lines in FIGURE 1 and shown more clearly in FIGURE 4, are provided in the outer surface of the inner barrel at regular intervals about its periphery. Below the slots, the outer diameter of the inner barrel is enlarged to form an intermediate section 30, bounded by an upper shoulder 31 and a lower shoulder 32 which seats against shoulder22 on the outer barrel. Slots 33 extend longitudinally through the intermediate section between the shoulders. The slots are shown by hidden lines in FIG- URES l and 4. External threads 34 are provided on the lower shank of the inner barrel below the bearing section. An axial passageway 35 extends downwardly from passageway 14 in the connecting member through the inner barrel.

The torsional unit in the apparatus shown in FIGURE 1 includes an inner sleeve 36 which seats about the upper end of the inner barrel and an outer sleeve 37 which fits into the upper end of the outer barrel. Torsion member 38 of rubber or similar elastic material which can be preloaded with from about 100 to about 1000 foot-pounds or more of torque is bonded to the surfaces of the sleeves. The bonding area on each sleeve should be made as large as possible in order to reduce stresses across the rubber-steel bond under high torsional loadings. The inner sleeve is welded or otherwise attached at its lower end to inner locking member 39 which is provided with slots that mate with and engage slots 29 on inner barrel 25. The outer sleeve is similarly welded or otherwise attached to an outer locking member 40 which is held in position with respect to the outer barrel by means of pins 41. The pins extend through holes in the outer barrel and slots 42 in the locking member and may be welded in place at their outer ends.

An elongated steel shoe 43 is connected to the lower end of the inner barrel below the bearing section and torsional unit. The shoe abuts against internal shoulder 23 in the outer barrel and projects downwardly below the slots 24 at the lower edge of the barrel. A passageway 44 extends from passageway 35 in the inner barrel into the lower part of the shoe, where nozzles 45 and 46 are located. The nozzles do not appear in FIGURE 1 of the drawing but can be seen in FIGURE 3. The nozzles may be of either the welded or replaceable type and will normally be lined with tungsten carbide or a similar erosion resistant material. Each nozzle is positioned to permit the discharge of a high velocity stream of drilling iluid against the formation at the bottom of the borehole. As can be seen from FIGURE 2 of the drawing, the shoe is provided with beveled edges'and is designed to turn through an angle of from about 1 to about 15 degrees within the lower section of the housing. The lower portion of the shoe contains an opening 47 near the axis of the tool to accommodate blades 48 and 49. The blades are held in place by pin 50 which extends through each blade and through the housing. A single pin is shown but a separate pin may be used for each blade if desired.

Each of the blades employed is an elongated member having an inner arm which fits into opening 47 in the lower surface of the shoe and an outer arm which extends upwardly about the shoe. The upper end of each blade is tapered and provided with a rounded projection 51, shown more clearly in FIGURES 5 and 6 of the drawing, which fits into slot 24 in the lower edge of the outer barrel. The blades include lower transverse surfaces 52 and gage surfaces 53 which extend outwardly beyond the outer barrel. Steel blades hard surfaced with a metallic matrix containing chips or particles of tungsten carbide or a similar material which serve as cutting elements are preferred. Diamonds and tungsten carbide inserts may be provided on the gage edges of the blades to increase resistance to wear and abrasion and thus prolong the life of the blades. The shoe extends outwardly behind each blade as shown in order to support the blades in the drilling position.

FIGURE 4 in the drawing illustrates a modification of the bit shown in FIGURE 1 in which a coil spring 55 is utilized in lieu of the elastic torsional member. The spring is connected at its upper end to an upper annular retainer 56 which is in turn welded or otherwise afiixed to the outer sleeve 37. The weld is indicated by reference numeral 57. As in the earlier embodiment, the outer sleeve is attached to outer locking member 40 which is held in place in the outer barrel by pins 41. The lower end of the spring is connected to lower annular retainer 58 which is welded to inner sleeve 36 and provided with slots which mesh with slots 29 in the inner barrel. Sockets 59 in the upper end of the inner sleeve are used to preload the torsional member. Similar sockets are provided in the embodiment of FIGURE 1 but do not appear in the drawing.

To assemble the tool shown in FIGURES 1 through 6 of the drawing, the blades 48 and 49 are first attached to the lower end of shoe 43 by means of pin 50. The pin is spot welded or otherwise locked in place. The outer barrel 20 with pins 41 welded in place is slipped downwardly ovre the shoe so that the ends of the blades fit into slots 24 and the shoe bears against shoulder 23. Inner barrel 25 is inserted in the upper part of the outer barrel and threaded into place. Slots 33 in the inner barrel permit it to slip past the pins 41 in the outer barrel. Inner sleeve 36 and outer sleeve '37, connected by torsional member 38, are positioned between the inner and outer barrel so that the outer sleeve engages the pins in the inner barrel and the inner sleeve is free to turn above the slots in the inner barrel. The inner sleeve is turned counter clockwise with respect to the outer barrel by means of a Wrench inserted in sockets 59 to load the torsional member. After the desired torque has been obtained, the inner and outer sleeves are moved-downwardly so that the inner sleeve engages the inner barrel within the slots 29. Connecting member 11 with packing 26 held by retainer 27 and bolt 28 is then positioned between the inner and outer barrels and threaded into place. The tool is now ready for use.

In utilizing the bit shown in FIGURES 1 through 6 of drawing, the tool is lowered into the borehole at the lower end of a rotary drill string. The torque exerted by torsional member 38 tends to rotate inner. barrel 25, shoe 43 and blades 48 and 49 in a clockwise direction with respect to outer barrel 20. Since the upper ends of the blades are retained in slots 24' in the outer barrel, the lower ends of the blades are held forward in the sharpening position shown in FIGURE 5 of the drawing. In this position, the trailing edges of a dull blade will extend below the leading edges as shown. The circulation of drilling fluid is then commenced. Weigh-t is applied to the bit and the drill string is rotated. The force exerted on the blades by the formation as the tool is rotated results in a counterclockwise torque which exceeds the torque exerted by torsional member 38. The outer barrel of the tool therefore rotates clockwise with respect to the inner barrel, shoe and blades until further rotation is stopped by contact between the upper section of the shoe and the lower section of the outer barrel. The resulting movement of the upper ends of the blades in slots 24 shifts the blades into the drilling position shown in FIGURE 6 of the drawing. It will be noted that there is a clearance angle under the trailing edge of each blade in this position. Drilling is then continued with the blades so positioned until a reduction in the drilling rate indicates that the clearance angle hasbeen reduced and that the blades have therefore become dull.

At this point, the weight on the drill bit is reduced from the normal 10,000 to 50,000 lbs. to about 5,000 lbs. or less by raising the drill string a short distance in the borehole. This reduces the force exerted on the blades as the tool is rotated and therefore produces a marked reduction in counterclockwise torque. In response tothe clockwise torque exerted by the torsional member in the tool, the inner barrel, shoe and blades move clockwise within the outer barrel. This results in a return of the blades to the sharpening position shown in FIGURE 5 of the drawing. The trailing edges of the dull blades extends below the leading edges. The tool is rotated under the low weight with the blades in the forward position for a period sutficient to grind off the trailing edges so that the lower surfaces of the blades are parallel to the formation. The circulation of drilling fluid may be interrupted and the rotary speed may be increased in order to accelerate sharpening. Particles of sand, powdered tungsten carbide or a similar material may also be circulated into the bottom of the borehole at the onsetof the sharpening operation' to increase friction between the blades and formation and further speed up grinding off of the trailing edges. Tests have shown that blades hard surfaced with tungsten carbide can readily be sharpened in shales and similar formations by rotating the bit at speeds between about 150 and 250 revolutions per minute for a period of from about 5 to about 20 minutes without circulating drilling fluid. The addition of abrasive particles from the surface is therefore generally unnecessary. After the blades have thus been sharpened, the weight on the tool is increased, the rotary speed is preferably reduced, and drilling is continued. Sharpening the blades in this manner significantly increases the drilling rates obtained and permits the use of the bit in hard formations where the blades of conventional drag bits quickly become dull and cannot be used.

FIGURES 7 through 12 of the drawing illustrate a further embodiment of the invention in which the weight and hydraulic force applied to the tool are regulated to con- 'trol the position of the blades and thus permit sharpening.

The bit depicted in FIGURE 7 includes a tubular steel outer barrel comprising an upper section 60 and a lower section 61 connected by threads 62. The upper section contains internal threads 63 by means of which the tool may be connected to the lower end of a rotary drill string. A snap ring 64 or similar retainer is inserted in a groove in the inner wall of the upper section below the threads to hold packing 65 in place above internal shoulder 66. The inner diameter of the upper section below the packing increases in two steps, forming shoulders 67 and 68 which face the lower end of the apparatus. The lower section of the outer barrel has a slightly smaller inside diameter atits upper end than does the upper section. Below an intermediate zone of enlarged internal diameter bounded by shoulders 69 and 70, the lower section has a bore of hexagonal cross-section as shown in FIGURE 9 of the drawing. Cam slots 71 are located in the lower edge of the lower section as depicted in FIGURES 11 and 12. As

shown, the upper portion of each slot extends forward in the direction of bit rotation but other slot arrangements may be utilized.

The inner barrel 72 in the embodiment shown in FIG- URES 7 through 12 is a tubular steel member containing an axial passageway 73 through which drilling fluid may be circulated. The inner barrel is located in the upper part of the tool and is provided with external shoulders which abut against shoulders 67 and 68 on the outer barrel to limit upward movement and against the upper edge of the lower section of the outer barrel to restrict downward movement.

Shoe 74 is connected to the lower end of the inner barrel by means of threads 75. The shoe is a hollow member of steel or similar material containing a passageway 76 which extends from passageway 73 in the inner barrel to nozzles 77 and 78, shown in FIGURES 8, 10, 11 and 12 of the drawing. The nozzles are again preferably lined with tungsten carbide or like material and are preferably set at an angle to the axis of the bit to permit optimum discharge of fluids against the formation. A recess 79 is provided in the lower surface of the shoe to accommodate blades 80 and 81. Each blade includes a gage edge 82 and a lower cutting edge 83 and is preferablyconstructed of steel hard surfaced with tungsten carbide or similar material. Pins 84, secured by spot welding or otherwise fastening them to the blades, extend through openings in the blades and shoe to hold the blades in place. The blades extend upwardly about the outer surface of the shoe into slot 71 in the lower section of the outer barrel. As can be seen in FIGURES 11 and 12, the slots and upper ends of the blades are shaped so that vertical movement of the barrel causes the blades to pivot about the pin and thus move forward or backward. The lower end of the shoe extends laterally behind each blade, as shown more clearly in FIGURE 10, thus reducing the free space in the'annulus near the lower end of the tool and preventing further blade movement as the tool is rotated against the formation. The lower section of the shoe assists in stablilizing the bit in the hole and permits better control of fluid circulation. Although the bit shown in the drawing is provided with two blades, it will be apparent that a greater or lesser number can be used.

The bit shown in FIGURES 7 through 12 is assembled by first inserting pin 84 through the openings in the blades and lower end of the shoe and spot welding or otherwise fastening it to the blades at its outer ends. Outer barrel lower section 61 is placed over the shoe so that the upper downwardly with respect to the outer barrel until the inner barrel rests against the lower section of the outer barrel. The movement of the outer barrel relative to the upper ends of the blades forces the lower ends of the blades forward into the sharpening position shown in FIGURE 11 of the drawing. The tool is lowered into place in this position. After the blades contact the formation and sufiicient weight has been applied, the outer barrel moves downwardly about the inner barrel and shoe into the position shown in FIGURE 7. Movement of the upper ends of the blades in the cam slots in the outer barrel forces the blades into the drilling position shown in FIGURE 12. Fluid is circulated downwardly through the bit and drilling is commenced by rotating the drill string.

When a reduction in drilling rate indicates that the blades of the bit shown in FIGURES 7 through 12 should be sharpened, the weight applied to the bit is reduced by raising the drill string at the surface. The pressure of the drilling fluid forces the inner barrel, shoe and blade assembly downwardly in the outer barrel, moving the blades forward into the sharpening position shown in FIGURE 11. The bit is then rotated at high speed against the formation in order to grind off the trailing edges of the blades and thus restore the clearance angle necessary to achieve high drilling rates. Abrasive particles or the like may again be circulated into the hole in order to accelerate sharpening if necessary. Thereafter, the weight on the bit is increased to move the blades back into the drilling position and permit resumption of the drilling operation.

FIGURES 13 through 19 of the drawing depict a further embodiment of the invention in which the blades are actuated by cams set in slots in the upper ends of the blades. The apparatus shown in FIGURE 13 includes a tubular steel connecting member provided with internal threads 91 near its upper end to permit attachment of the tool to the lower end of a rotary drill string and with internal threads 92 near its lower end. Attached to the lower end of the connecting member is a steel outer barrel made up of an upper section 93, an intermediate section 94 and a lower section 95. The three sections are connected by means of threads 96 and 97. The upper section of the outer barrel contains an upper internal shoulder 98 which serves to retain the packing used to effect the seal in the outer barrel and a lower shoulder 99 which restricts upward movement of other components of the tool with respect to the outer barrel. The inner diameter of the intermediate section is less than thatof the upper and lower sections, providing internal shoulders 100 and 101. The bore of the lower section is of hexagonal cross-section and contains longitudinal grooves 102 as shown in FIGURE 14 of the drawing to avoid trapping fluid within the apparatus. Openings 103 extend through the wall of the lower section near the lower end thereof.

Inner barrel 104 is positioned in the upper end of the outer barrel adjacent the packing 105 of rubber, plastic or similar resilient material. The packing is held in place by ring 106, set in a groove in the outer barrel. Shoulder 107 on the inner barrel seats against shoulder 99 on the outer barrel when the latter is in its lowermost position. The lower end of the inner barrel limits upward movement of the outer barrel by contacting shoulder 100. Axial passageway 108 through the inner barrel permits the introduction of drilling fluid into the lower part of the tool from the connecting member.

Shoe 109 is an elongated steel member connected to the lower end of the inner barrel by means of threads 110. The shoe includes an upper section above external shoulder 111 which passes through the intermediate section of the outer barrel, a center section of hexagonal cross section as shown in FIGURE 14 of the drawing, and a slotted section of generally circular cross section extending below the outer barrel. The lower end of the shoe below the circular section contains slots 112 within which blades 113 and 114 are positioned. The blades extend upwardly about the outer surface of the shoe and include outer or gage edges 115 and lower or drilling edges 116. Pins 117, only one of which is shown, hold the blades in place. Each blade contains an arcuate slot 118 which extends upwardly in the inner surface of the blade adjacent the shoe. Curved-cams 119 positioned in the slots are mounted on pin sections 120 of extension members 121. The extension members extend upwardly from the blades within slots in the outer surface of the shoe and are held in place by projections 122 which fit into openings 103 in the outer barrel. As shown in FIG- URES 15 and 18,the extension members are splined to hold them in place. Movement of the outer barrel of the tool relative to the shoe results in movement of the cams within the blade slots. This in turn forces the blades forward or backward, depending on the direction in which the barrel moves relative to the shoe. The blades may thus be positioned for drilling orfor sharpening by the application of weight to the bit.

Passageway 123 extends downwardly in the shoe from the inner barrel and communicates with nozzles 124 mounted in the lower part of the shoe. A sleeve of tungsten carbide or similar material 125 is mounted above each nozzle to reduce erosion. The nozzles themselves are preferably made of tungsten carbide. The nozzle lo cations with respect to the blades are shown in FIGURE 17 of the drawing. As can be seen from FIGURE 17, the lower portion of the shoe between the blades is enlarged to provide a pad behind each blade which serves to support the blade, stabilize the bit in the borehole, and divert the flow of drilling fluid adjacent the face of each blade as the fluid passes upwardly in the borehole annulus.

The tool shown in FIGURES 13 through 19 of the drawing is assembled by first connecting extension members 121 to the lower section 95 of the outer barrel by inserting projections 122 on the extension members into openings 103 from the inside. The lower section and extension members are then slipped downwardly over the upper end of the shoe so that the extension members will slide downwardly in the slots in the shoe. Intermediate section 94 of the outer barrel is connected to the lower section 95 by threads 97. Sections 94 and 95 may instead be welded together after machining if desired. The inner barrel 104 is then connected by threads 110 to the upper end of the shoe. After the inner barrel has been tightened in place, the upper section 93 of the outer barrel is lowered over the inner barrel and threaded onto the intermediate section 94 by means of threads 96. Packing 105 is installed in the space between the inner and outer barrels above shoulder 98 and ring 106 is installed to hold the packing in place. Connecting member 90 is attached to the upper end of the outer barrel by threads 92. After the upper part of the tool has thus been assembled, cams 119 are positioned on projections 12!) on the extension members and the blades 113 and 114 are fitted in place over the cams. Pins 117 are inserted through holes in the blades and lower portion of the shoe and held in place by welding or otherwise fastening the pins to the blades. If replaceable nozzles are employed, they may be installed at this time. Otherwise, the nozzle will normally be bonded within the shoe at the time the shoe is fabri- 'cated.

The bit shown in FIGURES 13 through 19 is utilized in much the same manner as the tools described earlier. As the assembled bit is lowered into the borehole, the shoe, inner barrel and blade assembly will be supported by shoulder 100 on the outer barrel. When the shoe is thus in its lower-most position with respect to the outer barrel, extension members 121 hold cams 119 in the position shown in FIGURE 19 of the drawing. When the assembly reaches the bottom of the borehole and weight is applied, the outer barrel moves downwardly about the shoe and inner barrel. This forces the extension members downwardly with respect to the shoe and moves the cam members downwardly in the blade slots. The blades therefore move back into the drilling position shown in FIGURE 17 of the drawing. Drilling may therefore be commenced as soon as the tool has been lowered in place and complete circulation of the drilling fluid has been established.

To sharpen the bit of FIGURES 13 through 19, the weight on the bit is reduced by lifting the drill string from the surface or by holding the string stationary and permitting the bit to drill ahead for a short distance with fluid circulating. In either case, the hydraulic pressure exerted by the drilling fluid causes the inner barrel, shoe and blade assembly to move downwardly with respect to the outer barrel and connecting member. The resultant movement of the cams within the blade slots forces the blades forward into the sharpening position. In this position, the trailing edges of the blades extend below the leading edges as shown in FIGURE 19. The bit is then rotated against the formation wit-h suflicient speed to Wear down the trailing edges of the blade until the lowerfsurface of each blade is substantially horizontal. Sufficient weight is then applied to the tool to move the outer barrel and connecting member downwardly about the shoe and inner barrel. This returns the blades to the drilling position and provides a small clearance angle beneath the trailing edge of each blade as shown in FIGURE 17. Drilling may then be resumed.

FIGURES 20 through 25 in the drawing illustrated two additional embodiments of the invention which are similar to that shown in FIGURES 7 through 12 but utilize difierent blade configurations and different blade motion. The tool shown in FIGURE 20 includes an outer barrel having an upper section 130 provided with means for attaching the bit to a rotary drill string and a lower section 131 containing slots 132 into which the upper ends of the blades fit. An inner barrel 133 is positioned within the upper part of the outer barrel and is connected to shoe 134 which projects below the outer barrel. The shoe and outer barrel include hexagonal sections as shown in the earlier embodiment or other means for preventing rotation of one member with respect to the other. Passageway 135 extends downwardly in the inner barrel and shoe to nozzles which do not appear in the drawing. The blades 136 and 137 utilized on this embodiment of the invention differ from those employed in the earlier embodiment in that they taper downwardly from the inner edges to the outer or gage edges and thus produce a convex surface at the bottom of the borehole during a drilling operation. Each blade is attached to the shoe by a pin 138 set at an angle to the longitudinal axis of the bit. The pin shown in FIGURE 20 is an integral part of the blade and is held in place in the shoe by means of a retaining bolt 139 which is threaded into a hole in the shoe and passes through a groove 140 in the upper end of the pin. Other systems for supporting the pins in the lower end of this shoe may be utilized.

The operation of the bit shown in FIGURES 20 through 22 of the drawing is similar to that of the tool depicted in FIGURES 7 through 12. During normal drilling operations, the outer barrel of the tool rests against the enlarged section of the shoe near the lower end of the assembly. The slots 132 in the outer barrel'hold the blades in a vertical position as shown in FIGURES 20 and 21. The leading edges at the bottom of the blades extend below the trailing edges, assuming that the blades are sharp, and thus acceptable drilling rates can generally be obtained. When the blades become dull and drilling rates decline,

the weight on the bit is reduced by raising the drill string.

or letting the bit drill ahead while the string is held in fixed position. As the inner barrel, shoe and blade assembly move downwardly with respect to the outer barrel, the upper ends of the blades in slots 132 are forced to the rear due to the shapes of the slots and upper ends of the blades. This turns the blades on pins 138. The inner edge at the lower end of each blade moves forward. At

' the same time, the leading edges are raised and the trailing edges are lowered as shown in FIGURE'22 so that the trailing edges contact the convex formation at the bottom of the borehole. The bit can now be rotated at high speed against the formation to wear away the trailing edges without damaging the leading edges, thus sharpening the blades. After the tool has been sharpened in this manner, the bit weight can be increased to return the blades to the normal drilling position.

The embodiment of the invention represented in FIG- URES 23 to 25 of the drawing is identical to that shown in FIGURES 20 through 22 except that the blades are tapered upwardly toward the gage edges and the slots in the outer barrel of the tool slope inthe opposite direction. In FIGURE 23, blades and 141 are attached to the shoe 142 by means of pin 143 which is held in place by bolt 144 passing through groove 145. The upper end of each blade is retained in a slot 146 in the outer barrel 147. The upper portions of the slots slope away from the leading edges of the blade, opposite the direction of rotation of the bit. With the outer barrel in a downward position with respect to the shoe and inner barrel, not shown, the blades are held in an essentially vertical position as depicted in FIGURE 24. The leading edges of the blade extend below the trailing edges and hence the blades are in position for drilling. Downward movement of the shoe and blade assembly within the outer barrel moves the upper ends of the blades forward. As the blades pivot about the pins used to support them, the inner edge at the lower end of each blade moves to the rear, as shown in FIGURE 25 of the drawing. This moves the trailing edges back into contactwith the concave formation at the bottom of the borehole and leaves the leading edges suspended above the forma tion. The bit can now be rotated at high speed to wear down the trailing edges and restore the clearance angle. Later lowering of the outer barrel with respect to the shoe and blade assembly will return the blade to the drilling position so that drilling operations can be continued.

FIGURES 26, 27 and 28 illustrate a further modification of the invention which permits the blades of a bit such as that shown in FIGURES 13 through 19 to be locked in the drilling position. This facilitates the use of the bit in shallow formations where the amount of weight that can be applied to the tool is limited and where it is sometimes diflicult to hold the blades in the drilling position. The tool shown in FIGURE 26 includes an outer barrel 160, a shoe 161, and a blade assembly similar to those shown in FIGURE 13. A tubular inner barrel 162 of steel or the like is connected to the upper end of the shoe by threads 163. The inner barrel contains lateral passages 164 and 165 which permit the entry of drilling fluid into axial passageway 166 extending through the inner barrel. Seal 167 is provided between the inner and outer barrels and is held in place by ring 168 set in a groove in the outer barrel. The upper end of the inner barrel includes an external flange 169 and an annular groove 170 located below the flange. A tubular housing member 171 is connected to the upper end of the outer barrel and extends upwardly about the inner barrel. Tubular supporting members 172 containing an internal shoulder 173 below lateral passages 174 and 175 is threaded into the upper end of the housing by threads 176. Latch members 177 are welded or otherwise mounted about the periphery of the supporting member below the lateral opening and extend downwardly to engage flange 169 in groove 170 on the inner barrel. Each latch member includes a projection 178 which extends into the vertical space between the supporting member and inner barrel above the flange. The inner corners at the tops of the projection are tapered as shown. The upper sections of the latch members are flexible to permit displacement of the projections outwardly so that the l flange is disengaged. A connecting member-179 is attached to the upper end of the housing member by threads 180 and is provided with an upper shank including threads 181 for attaching the tool to a rotary drill string.

The arrangement of the latch members in the apparatus is shown more clearly in FIGURE 27 of the drawing. A cylindrical latch release 1822 enlarged at the upper end to fit against shoulder 173 in the supporting member and provided with a spear 183 at its upper end is utilized to spread the latching members in the apparatus and thus disengage the flange 169 on the inner barrel. FIGURE 28 shows the latch release in place with the inner barrel disengaged. During the initial stages of a drilling operation in which the apparatus of FIGURES 26 through 28 is used, the inner barrel of the bit will normally be locked in place by means of the latching members 177. This holds the shoe and blade assembly in an upper position with respect to the outer barrel of the tool and prevents movement of the blade into the sharpening position. The bit weight and drilling fluid pressure may be varied as desired to secure maximum drilling rates. When it becomes necessary to sharpen the blades, the latch release 182 is dropped through the drill string and seats in the supporting member 172. The lower section of the latch release forces the latching members outwardly, releasing the inner barrel. Fluid is diverted through the lateral passages 174 and 175 is in the supporting member and passages 164 and 165 in the inner barrel. The pressure can be increased and the bit weight reduced to move the blades into the sharpening position after the latch release has been dropped into place. An increase in bit weight will return the blades to the normal drilling position with out removing the latch release. In the event that removal should become necessary for some reason, however, a conventional over-shot, not shown, can be lowered through the drill string at the end of a wire line to grasp the spear 183. The latch release can then be lifted to the drill string to the surface. In most instances it is desired to lock the blades in the drilling position only during the initial stages of the drilling operation and hence later removal of the latch release by means of a wire line is unnecessary.

It will be apparent from the foregoing that the invention provides a method and apparatus for rapidly sharpening the blades of a drag bit Without withdrawing the bit from the borehole. By moving the blades into a position such that the trailing edges contact the formation and the leading edges clear the bottom of the hole, the blades can be ground down to restore the desired clearance angle. By sharpening the blades at frequent intervals in this manner, considerably higher drilling rates than might otherwise be feasible can be obtained. The maintaining of sharp blades permits the drilling of hard formations in which conventional drag bits are often unsatisfactory. These and other advantages make the bit considerably more effective than drag bits available in the past.

What is claimed is:

1. A rotary drill bit which comprises:

(a) a tubular outer section provided with means near the upper end thereof for connecting said outer section to the lower end of a drill string;

(b) an elongated inner section supported within said outer section and depending therefrom, said inner section containing a longitudinal passageway for the discharge of drilling fluid beneath the bit, said outer section being movable with respect to said inner section between a first limiting position thereon and a second limiting position thereon, and said inner and outer sections including means for transmitting torque between said outer section and said inner section; and,

(c) a plurality of blades pivotally connected to said inner section near the lower end thereof and including leading edges which extend in contact with the formation beneath said bit in a first blade position and trailing edges which extend in contact with the formation beneath said bit in a second blade position, said blades being coupled to said outer section to pivctally move said blades between said first blade position and said second blade position in response to movement of said outer section between said first limiting position and said second limiting position with respect to said inner section.

2. A bit as defined by claim 1 wherein said outer section is rotatab-ly movable with respect to said inner section between said first limiting position and said second limiting position.

3. A bit as defined by claim 1 wherein said outer section is axially movable with respect to said inner section between said first limiting position and said second limiting position.

4. A bit as defined by claim 1 wherein said blades are pivotally connected to said inner section by means of pins extending in a plane normal to the longitudinal axes of said inner and outer sections.

5. A bit as defined by claim 1 wherein said blades are pivotally connected to said inner section by means of pins extending upwardly at an angle to the longitudinal axes of said inner and outer sections.

6. A bit as defined by claim 1 including means for locking said outer section in a fixed position with respect to said inner section and later releasing said outer section to permit movement with respect to said inner section.

7. A rotary drill bit comprising:

(a) a tubular outer section including means near the upper end thereof for connecting said outer section to the lower end of a drill string;

(b) an elongated inner section supported within and depending from said outer section, said inner section containing a longitudinal passageway for the discharge of drilling fiuid beneath the bit, said outer section being rotatable with respect to said inner section between a first limiting position and a second limiting position, and said inner and outer sections including means for transmitting torque between said outer section and said inner section;

(c) a torsion member interconnecting said inner and outer sections, said torsion member normally biasing said outer section in said second limiting position with respect to said inner section; and,

(d) a plurality of blades pivotally connected to said inner section near the lower end thereof, the upper ends of said blades engaging said outer section near the lower end thereof and said blades including leading edges which extend in contact with the formation beneath said bit when said outer section is in said first limiting position with respect to said inner section and trailing edges which extend in contact with the formation beneath said bit when said outer section is in said second limiting position with respect to said inner section.

8. A bit as defined by claim 7 wherein said torsion member comprises a coil spring.

9. A bit as defined by claim 7 wherein said torsion member is made of rubber.

10. A rotary drill bit which comprises:

' (a) a tubular outer section including means near the upper end thereof for connecting said outer section to the lower end of the drill string;

(-b) an elongated inner section supported within and depending from said outer section, said inner section containing a longitudinal passageway for the discharge of drilling fluid beneath the bit, said outer section being axially movable with respect to said inner section between a first limiting position and a second limiting position, and said inner and outer sections including means for transmitting torque between said outer section and said inner section; and,

(c) a plurality of blades pivotally connected to said inner section near the lower end thereof, the upper ends of said blades engaging said outer section near the lower end thereof and said blades including leading edges which extend in contact with the formation beneath said bit when said outer section is in said first limiting position with respect to said inner section and trailing edges which extend in contact with the formation beneath said bit when said outer section is in said second limiting position with respect to said inner section.

11. A bit as defined by claim wherein said blades are pivotally connected to said inner section by pins which extend upwardly at an angle to the longitudinal axes of said inner and outer sections and said leading and trailing edges of said blades extend upwardly from the inner edge to the gage edge of each blade.

12. A bit as defined by claim 10 wherein said blades are pivotally connected to said inner section by pins which extend upwardly at an angle to the longitudinal axes of said inner and outer sections and said leading and trailing edges of said blades extend upwardly from the gage edge to the inner edge of each blade.

13. A rotary drill bit which comprises:

(a) a tubular outer barrel provided with means near the upper end thereof for connecting said outer barrel to the lower end of a drill string;

(b) a tubular inner barrel positioned within said outer barrel, said outer barrel being movable with respect to said inner barrel between a first limiting position thereon and a second limiting position thereon;

(c) a shoe rigidly connected to said inner barrel and extending downwardly below said outer barrel, said inner barrel and shoe containing a longitudinal passageway for the discharge of drilling fluid beneath the bit and said outer barrel and said shoe including means for transmitting torque between said outer barrel and shoe; and,

(d) a plurality of blades pivotally connected to said shoe below said outer barrel, each of said blades being coupled to said outer barrel above the point at which said blade is pivotally connected to said shoe and each blade including a leading edge which extends in contact with the formation beneath said bit when said outer barrel is in said first limiting position with respect to said inner barrel and a trailing edge which extends in contact with the formation beneath said bit when said outer barrel is in said second limiting position with respect to said inner barrel.

14. A bit as defined by claim 13 wherein each of said blades is coupled to said outer barrel by means of a slot in said outer barrel into which the upper end of said blade extends.

15. A bit as defined by claim 13 wherein each of said blades is coupled to said outer barrel by means of a cam and connecting member.

16. A rotary drill bit which comprises:

(a) a tubular outer barrel provided with means near the upper end thereof for connecting said outer barrel to the lower end of a drill string;

(b) a tubular inner barrel positioned within said outer barrel, said outer barrel being axially movabe with respect to said inner barrel between a first limiting position thereon and a second limiting position thereon; r

(c) a shoe rigidly connected to said inner barrel and extending downwardly below said outer barrel, said inner barrel and shoe containing a longitudinal passageway for the discharge of drilling fluid beneath the bit and said outer barrel and shoe including means for transmitting torque between said outer barrel and shoe;

(d) a plurality of blades pivotally connected to said shoe below said outer barrel by means of pins extending in a plane normal to the longitudinal axes of said inner barrel and shoe, each of said blades containing a cam slot near the upper end thereof and including a leading edge which extends in contact with the formation beneath said bit in a first blade.

position and a trailing edge which extends in contact with the formation beneath said bit in a second blade position;

(e) cam members positioned in said slots in said blades, said blades pivoting about said pins between said first blade position and said second blade position 'in'response to movement of said cam members Within said slots; and,

(f) connecting member extending from said outer barrel above said blades to said cam members for moving said cam members in response to movement of said outer barrel between said first limiting position and said second limiting position with respect to said inner barrel.

17. A rotary drill bit which comprises: i

(a) a tubular outer barrel provided with means near the upper end thereof for connecting said outer barrel to the lower end of a drill string;

(b) a tubular inner barrel positioned within said outer barrel, said outer barrel being axially movable with respect to said inner barrel between a first limiting position thereon and a second limiting position thereon;

(c) a shoe rigidly connected to said inner barrel and extending downwardly below said outer barrel, said inner barrel and shoe containing a longitudinal passageway for the discharge of drilling fluid beneath the bit and .said outer barrel and shoe including means for transmitting torque between said outer barrel and shoe; and,

(d) a plurality of blades pivotally connected to said shoe below said outer barrel by means of pins extending in a plane normal to the longitudinal axes of said inner barrel and shoe, the upper ends of said blades above said pins extending into slots in said outer barrel near the lower end thereof and said blades including leading edges which extend in contact with the formation beneath said bit when said outer barrel is in said first limiting position with respect to said inner barrel and trailing edges which extend in contact with the formation beneath said bit when said outer barrel is in said second limiting position with respect to said inner barrel. 

1. A ROTARY DRILL BIT WHICH COMPRISES: (A) A TUBULAR OUTER SECTION PROVIDED WITH MEANS NEAR THE UPPER END THEREOF FOR CONNECTING SAID OUTER SECTION TO THE LOWER END OF A DRILL STRING; (B) AN ELONGATED INNER SECTION SUPPORTED WITHIN SAID OUTER SECTION AND DEPENDING THEREFROM, SAID INNER SECTION CONTAINING A LONGITUDINAL PASSAGEWAY FOR THE DISCHARGE OF DRILLING FLUID BENEATH THE BIT, SAID OUTER SECTION BEING MOVABLE WITH RESPECT TO SAID INNER SECTION BETWEEN A FIRST LIMITING POSITION THEREON AND A SECOND LIMITING POSITION THEREON, AND SAID INNER AND OUTER SECTIONS INCLUDING MEANS FOR TRANSMITTING TORQUE BETWEEN SAID OUTER SECTION AND SAID INNER SECTION; AND, (C) A PLURALITY OF BLADES PIVOTALLY CONNECTED TO SAID INNER SECTION NEAR THE LOWER END THEREOF AND INCLUDING LEADING EDGES WHICH EXTEND IN CONTACT WITH THE FORMATION BENEATH SAID BIT IN A FIRST BLADE POSITION AND TRAILING EDGES WHICH EXTEND IN CONTACT WITH THE FORMATION BENEATH SAID BIT IN A SECOND BLADE POSITION, SAID BLADES BEING COUPLED TO SAID OUTER SECTION TO PIVOTALLY MOVE SAID BLADES BETWEEN SAID FIRST BLADE POSITION AND SAID SECOND BLADE POSITION IN RESPONSE TO MOVEMENT OF SAID OUTER SECTION BETWEEN SAID FIRST LIMITING POSITION AND SAID SECOND LIMITING POSITION WITH RESPECT TO SAID INNER SECTION. 